I am in the process of wrapping the forced air heating ducts in my crawl space with a material that looks like bubblewrap with foil on both sides. Does anyone have any idea of how much savings this will be on my gas bill? The insullation is rated at R6, but I cannot relate this to actual savings in energy.
Be carefull it is not rated R6 if its the bubble wrap Im thinkng of, read it carefully, I think its a radiant barrier.
How much you save (if any) will depend on how much heat loss you're getting via the ducts to begin with. If they're already insulated, I suspect you might not see enough improvement to pay for the bubblewrap stuff (if it's what I'm thinking of, it's not cheap).
According to sherwindu :
It's very difficult to even try to estimate without having any knowledge of your installation/climate.
That said, chances are that it will be noticable savings if you compare equivalent periods.
In an externally vented/drafty crawlspace, you could be losing a _lot_ of heat from the bare ducts.
I don't see where he said they were bare ducts.
Ducts should be sealed with mastic first, fiberglass is better than bubble crap, higher R and much cheaper. Best way is slide on duct insulation. Bubble wrap I would not waste my time with and dought if it is R 6 more likely its R 1 or less per inch
Take the square foot surface of the duct, divide by R6, multiply by the ambient temperature, add the relative humidity and that is the percentage of your gas bill you save.
Edwin Pawlowski errs again:
... 70 ft^2 of R1 duct might lose (130-50)70ft^2/R1 = 5.6K Btu/h to a 50 F crawl space.
Wrapping the duct would save 70ft^2/R6x50F+50%RH = 633% of the gas bill? :-)
Wrapping the duct would reduce the heat loss to (130-50)70ft^2/R7 = 800 Btu/h.
Then again, with an airtight crawlspace above a vapor barrier, a lot of this heat could end up in the house. Maybe it's better to insulate the crawlspace.
Nick
Everyone Assumes its R6, did anyone read packing lit with that stuff, the ratings are not certified and state " Like R 6' its a BS rating just like " Insulating ceramic paint". Its a radiant barrier, foilfaced duct R 7 fiberglass is R 7 certified, plus radiant barrier. The price vs effectivness of bubble wrap to fiberglass make bubble wrap a joke. after all its just bubble wrap.
HAve you seen a conditioned crawl yet?
Before insulating your ducts that run thru the crawl space you will want to seal them first -- duct mastic is considered best though I've used the foil tape to seal all the seams. I've used foil tape that has held up very well over ten years now. Don't use regular duct tape -- it doesn't last. Seal the seams of the heating ducts as well as the return air ducts.
I've used the fiberglass duct insulation by Manville that I picked up at Lowes.
After sealing my ducts in my crawl space and then insulating all the heating and air return ducts I noticed a big improvement in the air flow and the heat of the air from the registers as far as how much there are a lot of SWAG methods that others have talked about but I do know I'm saving now for the life of the house and since I did the work myself my only costs were materials and time.
Are you wrapping the bubble wrap directly on the ductwork or are you putting an air space between the BW and the duct?
If you have not bought the R-6 then I would definitely think about something higher (according to the calculator).
Personally I would not use the stuff your installing. I would stick to fiberglass. I wrapped my fathers ducts in the garage. I used R-19 bats. Cut to length, lath to nail to the ceiling and tape the edges. He had a double garage, and the duct work was 2/3 of the width. Lowered the a/c bill $40 the first month. Heat was a little more. Sorry, it was a long time ago and I do not remember all of the numbers.
Good, altho the best way to do it is the following:
Seal all seals with at least two wraps of UL181-A-B metal tape with an acrylic adhesive, then, coat with elastomeric mastic. Once dry, cover with Owens Corning R7.6 duct wrap, maintaining the 2.5 inch rule, and then seal the seam with the proper tape and sealer tool. As an added measure, one should take and staple the tape to the wrap. The staple gun used for this isnt cheap...a good swedish made gun like we use runs about $100 and of course, uses a special staple for just this, turning the ends out of the staple and adding extra protection against the tape falling off.
Then you didn't do it correctly.
The Reflectix is supposed to have an air gap between the insulation and the duct. THAT'S what get's the wrap an R6.
The inner bubble wrap don't do anything.
applications, but
With Reflectix, you only get the full R-value if you place spacers under the wrap - read the directions carefully. The spacers are to provide a layer of trapped air between the wrap and the ducts. You are probably achiving significantly less than R-6.5 if you didn't do this, but another option is to wrap the ducts twice around with the wrap. In the real world, I can tell you that in a similar situation, crawl with vents, uninsulated floor, my coldest room increased in temperature approx 2-3 degrees, which is significant but not mind blowing. In our case, it solved a sticky problem of two rooms which had had a ceiling vaulted without a proper increase in the heating mechanics. I do however question the wrapping of the return ducts. In that case, the temperature differential between the duct air and the surround air is quite a bit less than the supply duct air and the crawl air, and therefore the heat loss is less, and less can be accomplished by wraping. Cetainly the payback is much longer. I would also partially block the air vents in the winter. Conditions are so dry then from heating (in the crawl) that there should not be a problem, and you will reduce the effect of cold air blowing up under your floors. Only in the attic would I NOT block the vents, as your moist heated air rises to that level.
sherw> Sorry for not being more explicit in describing my situation. The ducts are
Reflextic, yes Ive seen that crap, as you read it says " like R6" just like insulating paint says its "like R" whatever. The key work is "Like" it is not a certified rating, don`t you even wonder why Reflextic has different " like" ratings for different applications. Get a Cerfified insulation, one that is industry accepted and known, Fiberglass. And best is something designed for your job.
We have used the Reflectix in several aplications and it seems to do what is claimed. Best bet is to put a spiral of 2" wide Reflectix down the pipe, to provide additional air space. Then cover that with a full layer of reflectix and overlap the seams 2". Then tape the seams with foil tape.
R-6 fiberglass duct wrap also works well, as long as it is is not compressed. R-6 ductwrap is approx. 2.5" thick. If it is applied tight to the duct, so that it "Looks Nice", it compresses the insulation and can reduce the R-factor to as little as R-2. Measure the circumference of the duct and add 14.5". Cut that much duct wrap and wrap it around the duct with a 2" overlap. Staple and tape the seams. Use only tape rated UL-181 B-FX. The 14.5" add-on stretch out is the amount recommended by NAIMA (North American Insulation Manufacturers Association.) for 2.5" thick duct wrap installed on round duct.. Different thicknesses have different recommended stretchouts. For 2.5" thick wrap on rectangular duct the recommended add on is
12.5".Stretch
On cost alone fiberglass wins.
HomeOwnersHub website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.